Sound issues

Please also try the same with your HDMI connections, please un-plug and re-plug in.

Finally, please check the Apple TV to see if it has any firmware updates, look in Settings - System.

Another thing to try is:

• Unplug your modem for 2-3 minutes and restart.
• Unplug your router for 2-3 minutes and restart.
• Once again, unplug your Apple TV from it's power source for 2-3 minutes and restart and then retest.

While I don't think this could be the issue, it does not hurt to do this and might work.

Please first attempt unplugging the Apple TV from it's power source for about 2-3 minutes, then re-plug in and then retest.

That's awesome!

If your soundbar is HDMI-connected to your TV, then Apple TV 4K will send audio to the TV, which in turn can pass it through to the soundbar. That would be a setting on your TV, not on the Apple TV (which should be set for “TV Speakers”).